1. Field of the Invention
The present invention relates to an ink jet recording apparatus for recording by discharging ink from recording means to a recording material, and to a recovery method therefor.
2. Related Background Art
A recording apparatus having the function of a printer, copying machine, facsimile apparatus, or the like, or a recording apparatus used as an output equipment for a complex electronic equipment or a work station including a computer, word processor, or the like, is structured to record images on a sheet, plastic thin plate, or other recording material in accordance with image information. Such recording apparatuses are divided into those of an ink jet type, a wire-dot type, a thermal type, a laser beam type, or some other types in accordance with the recording methods adopted therefor.
Of the recording apparatuses described above, a recording apparatus of an ink jet type (hereinafter referred to as an ink jet recording apparatus) is such as to discharge ink from recording means (hereinafter referred to as a recording head) to a recording material, enabling the compact formation of its recording head; to record highly precise images at high speeds; and also, to record images on an ordinary sheet produced without any particular treatments, thus making it possible to execute recording at lower running costs. Also, being non-impact, the ink jet recording apparatus makes less noises in operation. Further, it is capable of recording color images with ease using ink of multiple colors, among other advantages. Of the ink jet recording apparatuses, particularly the apparatus of a line type, which uses full-multi recording means provided with many discharge ports arranged in the sheet width direction, is structured to be able to perform recording at enhanced speeds.
Then, an ink jet recording apparatus thus structured is further provided with a head recovery system to prevent the occurrence of clogging or the like in the liquid paths thereof. In a state that the discharge port formation surface of the recording head is capped, ink suction is executed by an appropriate sucking means arranged for the head recovery system. Thus, a discharge recovery process is conducted at a specific rate for removing overly viscous ink residing in the liquid paths or the like by causing such ink in the liquid paths to be exhausted forcibly form the ink discharge ports to obtain the enhanced reliability of printing operation.
Also, the recording head used for the ink jet recording apparatus described above is generally structured to be capable of discharging ink of one specific color by use of one recording head. Recently, however, there has been a head structured to be able to discharge ink in multiple colors by use of one and the same head with the provision of liquid chamber of a separate type.
In the latter case where the recording head is structured to discharge ink in multiple colors by use of only one head, it is possible to reduce the numbers of heads that may otherwise be required for printing color images using ink in multiple colors or for multi-level recording by use of ink of a similar color but different densities. In this case, therefore, the apparatus can be fabricated smaller at lower costs.
When an ink suction is operated to prevent the occurrence of head clogging, defective discharges, or the like, there is no possibility at all that any mixture of ink colors takes place after suction as far as only one monochromic ink remains in the interior of a cap to be used for sucking operation. . However, in such a case of using a recording head structured to be able to discharge ink in multiple colors within one and the same head with the provision of separated liquid chambers in it, such ink in multiple colors remain in the interior of the cap to be used for sucking operation. Therefore, a problem is encountered that a mixture of ink colors tends to occur when ink is discharged after the recovery by suction.
In order to make the most of a recording head integrally formed for use of multiple colors as described above (that is, to make-the main body smaller), it is preferable to arrange a structure so that the same type of a recovery operation as adopted for use of a monochromic head is still made available for a suction or any other recovery operation that is characteristic of an ink jet recording method. In other words, it is desirable to suck ink of all colors from nozzles by one suction for recovery instead of repeating suction several times per color. However, due to incapability of controlling irregular flows of ink in the cap at the time of sucking such recording head as integrally formed for use of multiple colors, there is an irregular occurrence of problem that the ink having been sucked from nozzles used for one color enters the nozzles of the other colors. Also, it is usually practiced that the discharge port surface is wiped by an elastic wiper after suction in order to remove ink and other particles remaining on the discharge port surface of the head. However, this wiping operation causes mixed ink to be pressed so that it may enter the nozzles. These conditions appear as a resultant discoloration (hereafter referred to as mixed colors) on the portion where writing begins in each color after the execution of the recovery.
In order to prevent the occurrence of the mixed colors, there is a need for removing each ink that may result in such mixed colors from the respective nozzles by the application of predischarges. Those amounts of ink to be removed by the application of predischarges are not used for printing directly. In a sense, it is a wasteful use of ink. Therefore, it is desirable to suppress the execution of predischarges to the least possible frequency.
The inventor et al hereof have studied the possibility to provide means for performing the removal of mixed colors with the least possible consumption of ink after suction, which is applicable to a four-color integrated recording head. As a result, it is found effective to repeat predischarges by combining the predischarges from all the nozzles, and predischarges only from the several nozzles on the respective end portions. The present invention is designed on the basis of such studies and results thereof.
It is one of the objectives of the present invention to provide an ink jet recording apparatus capable of effectuating the removal of mixed colors on the portions where writing begins in each color with the least possible ink consumption when operating the predischarges after suction, which are required to recover the discharge performance of an integrated ink jet recording head for use of multiple colors.
In accordance with the present invention, an ink jet recording apparatus using an integrated ink jet recording head for use of multiple colors is characterized in that after sucking operation, predischarges are executed at least from all the ports for discharging relatively thin ink by discharging such ink therefrom, only from the discharge ports on the end portions of the respective discharge ports, and from all the discharge ports in that order.
In this way, by executing predischarges with comparatively small consumption of ink, it is possible to recover the discharge performance of the recording head, and prevent the occurrence of the mixed colors on the portions where writing begins in each color after the recovery.
Also, in consideration of the technical problems encountered in the prior art, it is another object of the present invention to provide an ink jet recording apparatus capable of recording in high quality stably at all times by effectively removing the mixed colors after suction without consuming ink wastefully for an integrated ink jet recording head of a separated liquid chamber type, which is arranged to discharge ink in multiple colors within one and the same head.
In the ink jet head of a separated liquid chamber type, which is capable of discharging ink in multiple colors within one and the same head, if the negative pressures in the ink tanks for the respective colors are different, ink of other colors are drawn from ink discharge ports to the common liquid chamber through the liquid paths, and are caused to mix with ink of one color in the tank whose negative pressure is the highest; hence mixed colors taking place when ink is sucked from the ink discharge port array capped by capping means.
In accordance with the present invention, however, the negative pressure exerted in the ink tank for each color is detected by controlling means, and after suction by use of capping means, the number of predischarges is changed per ink discharge array for each color in accordance with the differences of negative pressure from the minimum negative pressure in the ink tank. In this way, it is possible to remove the mixed colors after suction without the wasteful use of ink for required predischarges.